Natural product for resisting potato scab as well as preparation method and application of natural product

Abstract

The invention discloses a potato scab resistant natural product as well as a preparation method and application thereof. The natural product chain is any compound of lateritic acid A-D, and the structural formula of the natural product chain is shown in the specification. The preparation method comprises the following steps: fermenting streptomyces sp. FXJ1.172, and separating the fermented product, so as to obtain the chain lateritic acid A-D. The chain lateritic acid A-D is obtained. The inventor finds that the compound has a good inhibition effect on streptomycete pathogenic strains causing potato scab through research, and further plant pot experiment shows that the compound can effectively prevent and control the potato scab and reduce the disease degree.

Description

Technical Field

[0001] The invention belongs to the field of medicine, and in particular relates to a natural product for resisting potato scab, and a preparation method and application thereof. Background Art

[0002] Potato is the world's second most important food security crop after rice and wheat. However, its production is threatened by a variety of plant pathogens. Among them, potato common scab (PCS) is a soil-borne and seed-borne disease caused by Streptomyces scabies and related plant pathogenic Streptomyces. PCS forms necrotic lesions on potato tubers, greatly reducing the market value of potato crops and thus causing catastrophic economic losses. Despite decades of research and exploration of treatment methods for PCS, the disease remains largely difficult to control, and potato growers around the world are in urgent need of new pesticides or biological control agents to address this stubborn disease.

[0003] Actinomycetes are a class of Gram-positive bacteria with high G+C content (69-78%), which have complex morphological development and differentiation processes and rich secondary metabolite synthesis capabilities. They are widely distributed in various habitats such as soil, ocean, and plants. Streptomyces is a large and more advanced species among actinomycetes. It has a variety of secondary metabolic pathways and is the main source of natural products. The secondary metabolites produced by Streptomyces account for more than one-third of the total number of microbial active natural products and have broad-spectrum activities, such as antibacterial, antifungal, antiparasitic, antitumor, and immunosuppressive agents, and are widely used in medicine, agriculture, and animal husbandry. Summary of the invention

[0004] One object of the present invention is to provide a series of natural product chain red clay acids and preparation methods.

[0005] The natural product streptolateritic acid provided by the present invention is any compound of streptolateritic acids AD, and its structural formula is as follows:

[0006]

[0007] R=H:streptolateritic acid A(1)R=OH:streptolateritic acid C(3)

[0008]

[0009] R=H:streptolateritic acid B(2)R=OH:streptolateritic acid D(4)

[0010] The preparation method of the natural product streptomyces acid AD provided by the present invention comprises the following steps: fermenting Streptomyces sp. FXJ1.172 to obtain a fermentation product; and separating the fermentation product to obtain the streptomyces acid AD.

[0011] The fermentation conditions may specifically be: 28° C., 220 rpm shaking culture for 10 days.

[0012] The culture medium used in the fermentation is a liquid SSC culture medium. The raw materials added to each liter of the liquid SSC culture medium are as follows: 20g of soluble starch, 10g of soybean powder, 5g of calcium carbonate, and the balance is water; carbonyl cyanide 3-chlorophenylhydrazone (CCCP) is also added to the liquid SSC culture medium, and its final concentration is 1μg / mL.

[0013] The fermentation can be specifically performed as follows: 2 mL of the seed culture is transferred to a 500 mL Erlenmeyer flask containing 200 mL of liquid SSC medium, carbonyl cyanide 3-chlorophenylhydrazine (CCCP) is added to make its final concentration 1 μg / mL, and the fermentation is continued at 220 rpm on a constant temperature shaker at 28°C for 10 days.

[0014] The seed culture may be specifically OD 600nm =0.6-0.8 of seed culture.

[0015] The preparation method of the seed culture can be specifically as follows: take 1 mL of Streptomyces sp. FXJ1.172 spore suspension (spore concentration is about 2.5×10 6 CFU / mL) was inoculated into a 50 mL centrifuge tube containing 10 mL of liquid TSB medium and activated on a 28°C constant temperature shaker at 220 rpm for 48 h to serve as a seed culture.

[0016] The raw materials added to each liter of the liquid TSB medium are as follows: 17 g tryptone, 3 g soybean hydrolysate, 2.5 g glucose, 5 g NaCl, and 1 g K 2 HPO 4 2.5, the balance is water, pH 7.1-7.5.

[0017] Specifically, a method for preparing the natural product red clay acid AD comprises the following steps:

[0018] 1) fermenting Streptomyces sp. FXJ1.172 to obtain a fermentation product;

[0019] 2) centrifuging the fermented product to collect mycelium and supernatant respectively; extracting the mycelium with anhydrous ethanol to collect ethanol extract; extracting the supernatant with ethyl acetate to collect ethyl acetate extract;

[0020] 3) respectively concentrating the ethanol extract and the ethyl acetate extract to dryness under reduced pressure, combining the concentrates, dissolving them in methanol, centrifuging them, and taking the supernatant;

[0021] 4) The supernatant is separated by high performance liquid chromatography to obtain the streptotric acid AD.

[0022] In step 2) of the above method, the ratio of the mycelium to anhydrous ethanol is 20 g: 200 mL, and the anhydrous ethanol is used for extraction overnight; the supernatant is extracted with an equal volume of ethyl acetate, and the ethyl acetate extraction is carried out for 3 hours.

[0023] In step 3) of the above method, the ratio of the combined concentrate to methanol is 0.5 g:2 mL.

[0024] In step 4) of the above method, the chromatographic conditions of the high performance liquid chromatography are:

[0025] The chromatographic column was a Waters Xbridge octyl decyl silane column, 4.6 × 150 mm, 5 μm;

[0026] Flow rate: 1.0ml / min;

[0027] Linear gradient elution was performed using a binary solvent system of water as phase A and methanol as phase B;

[0028] The gradient elution conditions were as follows:

[0029]

[0030] Detector: Diode array detector, screening monitoring absorption wavelengths between 190 and 800 nm.

[0031] Elatioric acid A (retention time = 16.2 min), Elatioric acid B (retention time = 16.3 min), Elatioric acid C (retention time = 14.2 min) and Elatioric acid D (retention time = 14.3 min) were obtained. The eluates were collected at the above retention times, concentrated and dried to obtain the above corresponding compounds.

[0032] Specifically, another method for preparing natural product red clay acid AD comprises the following steps:

[0033] a) fermenting Streptomyces sp. FXJ1.172 to obtain a fermentation product;

[0034] b) centrifuging the fermented product to collect mycelium; extracting the mycelium with anhydrous ethanol to collect the ethanol extract;

[0035] c) concentrating and drying the ethanol extract to obtain a crude extract, and purifying the crude extract on a silica gel column (100-200 mesh) using CHCl 3 :CH 3 Gradient elution was performed with a mobile phase having an OH volume ratio from 95:5 to 70:30, and all eluted fractions were collected;

[0036] d) purifying the eluted fraction using a Sephadex LH-20 gel column, isocratically eluting with methanol, and collecting the methanol eluted fraction;

[0037] e) separating the methanol elution component by reverse phase high performance liquid chromatography to obtain the erythritol acid AD.

[0038] In step b) of the above method, the ratio of the mycelium to anhydrous ethanol is 1000 g:10 L, and the extraction time can be 12 hours.

[0039] In step e) of the above method, the chromatographic conditions of the high performance liquid chromatography are:

[0040] The chromatographic column was a Supelco Ascentis C18 column, 100 × 21.1 mm, 5 μm;

[0041] Mobile phase: acetonitrile / water (37:63, v / v), flow rate 2.0 mL / min;

[0042] Detector: diode array detector;

[0043] Detection wavelength: 220nm;

[0044] HPLC retention time of the final product: erythritol acid A retention time = 9.2 min, erythritol acid B retention time = 11.1 min, erythritol acid C retention time = 6.0 min, erythritol acid D retention time = 7.4 min.

[0045] Another object of the present invention is to provide the application of the aforementioned erythritol acid AD.

[0046] The application provided by the present invention is the application of the streptotriac acid AD in the preparation of antibacterial drugs or in the prevention and treatment of potato scab.

[0047] Further, the antibacterial drug can inhibit the Streptomyces pathogenic bacteria that cause potato scab. Further, the potato scab is caused by Streptomyces pathogenic bacteria. The Streptomyces pathogenic bacteria are specifically such as: Streptomyces cesscabiei CGMCC 4.1765, Streptomyces fimicarius CGMCC4.1836, Streptomyces luridiscabiei CGMCC 4.3490.

[0048] Another object of the present invention is to provide an antibacterial drug.

[0049] The antibacterial drug provided by the present invention comprises at least one compound of the above-mentioned streptoeric acid AD.

[0050] Furthermore, the antibacterial drug can inhibit the Streptomyces pathogenic bacteria that cause potato scab.

[0051] The invention also provides a method for preventing and treating potato scab.

[0052] The method for preventing and controlling potato scab provided by the present invention is to apply an effective amount of at least one compound of redrutic acid AD to potato crops, seeds of potato crops, soil or cultivation carriers.

[0053] The Streptomyces sp. FXJ1.172 used in the present invention is a strain of Streptomyces isolated from a red soil sample in Jiangxi Province in the laboratory, and has good biological activity. The inventors isolated a series of natural products with new structures, streptolateritic acids AD, from the strain by optimizing the fermentation conditions, and found that the compounds have a good inhibitory effect on the pathogenic strains of Streptomyces that cause potato scab. Further plant pot experiments show that the compounds can effectively prevent and control the occurrence of potato scab and reduce the degree of the disease. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a growth morphology diagram of the strain Streptomyces sp. FXJ1.172;

[0055] Figure 2 is the HPLC chromatogram of streptotriac acid A–D;

[0056] Figure 3 is the high-resolution mass spectrum of eritic acid A–D;

[0057] Figure 4 For red clay acid A 1H NMR spectrum (500 MHz, solvent: CD 3 OD);

[0058] Figure 5 For red clay acid A 13 C NMR spectrum (125 MHz, solvent: CD 3 OD);

[0059] Figure 6 Dept135 NMR spectrum of erythritol acid A (500 MHz, solvent: CD 3 OD);

[0060] Figure 7 COSY spectrum of erythritol acid A (500 MHz, solvent: CD 3 OD);

[0061] Figure 8 HSQC spectrum of erythritol acid A (500 MHz, solvent: CD 3 OD);

[0062] Fig. 9 The HMBC spectrum of erythritol acid A (500 MHz, solvent: CD 3 OD);

[0063] Fig.10 NOESY spectrum of erythritol acid A (500 MHz, solvent: CD 3 OD);

[0064] Fig.11 For red clay acid B 1 H NMR spectrum (500 MHz, solvent: CD 3 OD);

[0065] Fig.12 For red clay acid B 13 C NMR spectrum (125 MHz, solvent: CD 3 OD);

[0066] Fig.13 For the chain red clay acid C 1 H NMR spectrum (500 MHz, solvent: CD 3 OD);

[0067] Fig.14 For the chain red clay acid C 13 C NMR spectrum (125 MHz, solvent: CD 3 OD);

[0068] Fig.15 For the chain red clay acid D 1H NMR spectrum (500 MHz, solvent: CD 3 OD);

[0069] Fig.16 For the chain red clay acid D 13 C NMR spectrum (125 MHz, solvent: CD 3 OD);

[0070] Fig.17 This is the antibacterial effect diagram of streptotriac acid A–D against three strains of potato scab pathogenic Streptomyces and Streptomyces FXJ1.172;

[0071] Fig.18 The inhibitory effects of streptocolic acid A and C on common potato scab in a laboratory greenhouse; (A) negative control (sterile water), showing no common scab symptoms; (B) positive control (S. scabiei CGMCC4.1765 T ), showing common scab symptoms; (CD) added inoculated seeds S. scabiei 4.1765 at 6 hours (attachment period) and 14 days (infection period) T Then, erythritol A (4 μg mL –1 ); (EF) at 6 h (attachment phase) and 14 days (infection phase) after addition of seed-inoculated S. scabiei 4.1765 T Then, add erythritol C (16 μg mL –1 ). DETAILED DESCRIPTION

[0072] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods described are conventional methods unless otherwise specified. The raw materials described can be obtained from public commercial channels unless otherwise specified.

[0073] The Streptomyces sp. FXJ1.172 used in the following examples is the Streptomyces sp. FXJ1.172 recorded in the following document: Liu M, Liu N, Shang F, Huang Y: Activation and identification of NC-1, a cryptic cyclodepsipeptide from red soil-derived Streptomyces sp. FXJ1.172. Eur J Org Chem, 2016, Jun 19; 2016(23): 3943-3948., which is publicly available from the applicant and can only be used to repeat the experiments of the present invention.

[0074] The growth morphology of the Streptomyces sp. FXJ1.172 is shown in the figure below: Figure 1 shown.

[0075] Example 1. Fermentation method for preparing eritic acid (small-scale fermentation and metabolite analysis)

[0076] Take an appropriate amount (1 mL) of Streptomyces sp.FXJ1.172 spore suspension (spore concentration is about 2.5×10 6 CFU / mL) was inoculated into 10 mL of liquid TSB medium (containing 1.7% tryptone, 0.3% soybean hydrolysate, 0.25% glucose, 0.5% NaCl, K 2 HPO 4 0.25%, pH 7.1-7.5) in a 50 mL centrifuge tube and activated on a 28°C constant temperature shaker at 220 rpm for 48 h as the seed culture (OD 600nm =0.6-0.8). Then transfer 2mL of the seed culture to a 500mL Erlenmeyer flask containing 200mL of liquid SSC medium (containing 2% soluble starch, 1% soy flour, and 0.5% calcium carbonate), and add carbonyl cyanide 3-chlorophenylhydrazine (CCCP, final concentration of 1μg / mL). Continue fermentation for 10 days at 220rpm on a 28°C constant temperature shaker. After the fermentation is completed, spin centrifuge 200mL of fermentation broth at 5,000rpm for 15 minutes to separate the mycelium and the supernatant. Add 200mL of anhydrous ethanol to the mycelium for overnight extraction, and add an equal volume of ethyl acetate to the supernatant for extraction for 3 hours. Filter and separate the anhydrous ethanol and ethyl acetate parts and concentrate them to dryness under reduced pressure respectively, dissolve and combine them with 2ml of methanol, centrifuge at 12000rpm for 10min, and take the supernatant for standby use.

[0077] High performance liquid chromatography (HPLC) detection:

[0078] Sample volume: 20 μl

[0079] Detection wavelength: streptavidin (254 nm).

[0080] HPLC analysis was performed on a Shimadzu Prominence HPLC system using a Waters Xbridge octyl decyl silane column (4.6×150 mm, 5 μm). The sample injection volume was 20 μL. A binary solvent system with water as phase A and methanol as phase B was used for gradient elution.

[0081] Mobile phase: A: methanol; B: water; flow rate: 1.0 ml / min;

[0082] Elution conditions: linear gradient elution

[0083]

[0084] By screening the monitoring absorption wavelength between 190 and 800 nm with a diode array detector, erythritol A (retention time = 16.2 min), erythritol B (retention time = 16.3 min), erythritol C (retention time = 14.2 min) and erythritol D (retention time = 14.3 min) were obtained. The chromatograms are shown in FIG. Figure 2 The eluate was collected at the above retention time and then concentrated and dried to obtain the above compound.

[0085] Example 2: Fermentation method for preparing erythritic acid (mass fermentation and separation and purification)

[0086] 2 mL of Streptomyces FXJ1.172 seed culture (same as Example 1) was cultured in SSC liquid medium (500 mL conical flask 50×200 mL, totaling 10 L) with CCCP added (final concentration of 1 μg / mL) at 28°C and 220 rpm for 10 days. After the fermentation, the mycelium was harvested by centrifugation at 5000 rpm for 15 minutes, and extracted with 10 L of ethanol at room temperature for 12 hours. The organic extract was filtered using a Buchner funnel and dried using a rotary evaporator to obtain 100 g of crude extract. 100 g of silica gel powder (Qingdao Ocean Chemical, specification 100-200 mesh, item number CXGJF-03-N3) was added and stirred evenly, and after filling to form a silica gel column, CHCl was used on it. 3 :CH 3 The elution was performed by gradient elution with a mobile phase having a volume ratio of 95:5 to 70:30. All eluted fractions were collected, combined, concentrated to 10 mL, and then added to a Sephadex LH-20 gel column. 3 OH to remove fatty acids and other lipophilic impurities.

[0087] A Supelco Ascentis C18 column (100×21.1 mm, 5 μm) was connected to a Shimadzu SPD-M20A instrument, with acetonitrile / water (37:63, v / v) as the mobile phase, a flow rate of 2.0 mL / min, and a PDA detector to detect the absorbance at 220 nm. The HPLC retention time and the obtained mass of the final product were as follows: erythritol A (7.2 mg, retention time = 9.2 min), erythritol B (1.8 mg, retention time = 11.1 min), erythritol C (7.4 mg, retention time = 6.0 min), and erythritol D (1.8 mg, retention time = 7.4 min).

[0088] Erythritol A(1):colorless solid;[α] 25 D +39.69(c=0.010,CH 3 OH); UV / vis(CH 3 OH)λ max (logε)208(2.81)nm; IR(neat)νmax 3288,2964,2926,2869,1702,1649,1418,1388,1287,1249,1023,969cm -1 ; HRESIMS m / z 587.2848[MH] - (calcd for C 32 H 44 O 10 ,587.2856).

[0089] Erythritol B(2):colorless solid;[α] 25 D +43.33(c=0.003,CH 3 OH); UV / vis(CH 3 OH)λ max (logε)206(2.38)nm; IR(neat)νmax 3284,2963,2932,2867,1702,1655,1442,1413,1388,1283,1251,1025,970cm -1 ; HRESIMS m / z 587.2849[MH] - (calcd for C 32 H 44 O 10 ,587.2856).

[0090] Erythritol C(3):colorless solid; [α] 25 D +23.36(c=0.013,CH 3 OH); UV / vis(CH 3 OH)λ max (logε)207(2.80)nm; IR(neat)νmax 3288,2980,2959,2865,1708,1651,1436,1386,1226,1025,973cm -1 ; HRESIMS m / z 603.2820[MH] - (calcd for C 32 H 44 O11 ,603.2806).

[0091] Erythritol D(4):colorless solid;[α] 25 D +32.22(c=0.003,CH 3 OH); UV / vis(CH 3 OH)λ max (logε)206(2.63)nm; IR(neat)νmax 3285,2975,2867,1703,1652,1583,1439,1414,1286,1224,1026,970cm -1 ; HRESIMS m / z 603.2811[MH] - (calcd for C 32 H 44 O 11 ,603.2806).

[0092] The high resolution mass spectra of erythritol A–D are shown in Figure 3 ;

[0093] The structural identification map of streptotriac acid A is shown in Figure 4-10 ;

[0094] The structural identification map of erythritol B is shown in Figure 11-12 ;

[0095] The structural identification map of erythritol C is shown in Figure 13-14 ;

[0096] The structural identification map of erythritol D is shown in Figure 15-16 .

[0097] Example 3: Determination of antibacterial activity of streptavidin AD

[0098] The modified microbroth dilution method was used to determine the minimum inhibitory concentration (MIC) of aerobic actinomycetes. The freeze-dried streptolateritic acids AD powder was initially dissolved in DMSO and then diluted with sterile water to a 2% DMSO solution for testing. 50 μL of 0.5×10 6CFU / mL of pathogenic Streptomyces culture was added with an equal volume of compound solution and cultured at 28°C for 48h. Antimicrobial susceptibility was determined in the range of compound concentrations from 0.125μg / mL to 128μg / mL using the doubling dilution method. MIC values ​​were obtained by turbidity analysis. All experiments were performed with three biological replicates, and the median was taken as the MIC value. Ampicillin, ciprofloxacin, chloramphenicol, piperacillin, rifampicin, tetracycline, and vancomycin were used as positive controls.

[0099] The strains evaluated in this example include: Streptomyces scabiei CGMCC4.1765 T , Streptomyces fimicarius CGMCC 4.1836, and Streptomyces luridiscabiei CGMCC 4.3490 were purchased from China General Microbiological Culture Collection Center. The evaluation results are shown in Table 1.

[0100] Table 1 Minimum inhibitory concentrations of streptomyces AD and some antibiotics against three strains of Streptomyces pathogenic to potato scab

[0101]

[0102]

[0103] The antibacterial activity evaluation showed that compared with the control antibiotics, streptotrichum acid AD showed similar or better inhibitory activity than the control antibiotics. Among them, the inhibitory ability of A / B, which was not hydroxylated at the C23 position, was stronger than that of C / D, which was hydroxylated.

[0104] Depend on Figure 1 The inhibition zone results showed that streptotriac acid AD had a good inhibitory effect on the growth of the three potato scab pathogens (CGMCC4.1765, CGMCC 4.1836, CGMCC 4.3490), but had no obvious inhibitory effect on the producing bacteria themselves (FXJ1.172).

[0105] Example 3: Testing the inhibitory effect of erythritol A or C on potato scab at the plant level through a potato pot experiment

[0106] Potato pot experiment was used to test the control of scab in potato laboratory pots. The experiment was carried out in a greenhouse. 10mL of S. scabiei CGMCC 4.1765 was injected into the roots of virus-free potato seedlings. T Bacterial suspension (concentration 10 9CFU / mL) to ensure that potatoes are infected with scab. 6h (attachment period) and 14d (infection period) after inoculation of S. scabiei in the experimental group, 10mL of chelidonic acid A (concentration of 4μg / mL) or chelidonic acid C (concentration of 16μg / mL) was injected into the root of each seedling, and the control group added an equal amount of sterile water. According to the growth of the plants, the same amount of water was added on time, the day and night temperature was 23℃ / 18℃, the relative humidity was 70%, and the light intensity was 1000lux. Cultivate until the potato tuber stage (about 90d), harvest the potatoes, rinse the tubers with a diameter of more than 3cm under tap water, and score the percentage of the tuber area covered by scab according to the potato scab disease grading standard, and calculate the disease index and incidence rate of the experimental group and the control group, and calculate the prevention effect.

[0107] The disease index was calculated according to the following formula:

[0108] Disease index=[∑(n×1+n×2+n×3+n×4+n×5) / (N×5)]×100. (n=number of tubers corresponding to the numerical grade. N=total number of potato tubersassessed).

[0109] The 1-5 score table refers to the percentage of the area infected by scab:

[0110] 0: no scab symptoms; 1: 0–12.5% ​​of the area infected; 2: 12.6–25% of the area infected; 3: 26–50% of the area infected; 4: 51–75% of the area infected; 5: 76–100% of the area infected.

[0111] Preventive effect = (disease index of the control group - disease index of the treated group) / disease index of the control group × 100%.

[0112] The evaluation results of the control effect of streptotriac acid on potato scab are shown in Table 2.

[0113] Table 2 Evaluation of the control effect of erythritol on potato scab

[0114]

[0115] Note: 4.1765 is the pathogenic strain of potato scab. Add the compound red clay acid A or C 6 hours or 14 days after the virus-free potato seedlings are inoculated with scab fungi, and harvest the potatoes 90 days later to evaluate the control effect.

[0116] The inhibitory effects of erythritol A and C on common potato scab in a laboratory greenhouse Fig.18As shown in the figure, both eritic acid A and eritic acid C can effectively inhibit potato scab. This shows that the eritic acid provided by the present invention can effectively prevent and control the occurrence of potato scab and reduce the disease at the plant level.

Claims

1. The natural product erythritol acid is any compound of erythritol acid AD, and its structural formula is as follows:

2. The method for preparing the streptomyces acid AD according to claim 1, comprising the following steps: fermenting Streptomyces FXJ1.172 to obtain a fermentation product; and separating the fermentation product to obtain the streptomyces acid AD.

3. The preparation method according to claim 2, characterized in that: The fermentation conditions are as follows: 28°C, 220rpm shaking culture for 10 days; Or, in the step 1), the culture medium used for the fermentation is a liquid SSC culture medium, and the raw materials added to each liter of the liquid SSC culture medium are as follows: 20g soluble starch, 10g soybean powder, 5g calcium carbonate, and the balance is water; carbonyl cyanide 3-chlorophenylhydrazine is also added to the liquid SSC culture medium to a final concentration of 1μg / mL.

4. The method for preparing the streptavidin acid AD according to claim 2 or 3, comprising the following steps: 1) fermenting Streptomyces FXJ1.172 to obtain a fermentation product; 2) centrifuging the fermented product to collect mycelium and supernatant respectively; extracting the mycelium with anhydrous ethanol to collect ethanol extract; extracting the supernatant with ethyl acetate, and collecting the ethyl acetate extract; 3) respectively concentrating the ethanol extract and the ethyl acetate extract to dryness under reduced pressure, combining the concentrates, dissolving them in methanol, centrifuging them, and taking the supernatant; 4) Separating the supernatant by high performance liquid chromatography to obtain the streptotric acid AD.

5. The preparation method according to claim 4, characterized in that: In the step 2), the mycelium and anhydrous ethanol are mixed in a ratio of 20 g: 200 mL, and the anhydrous ethanol is used for overnight extraction; the supernatant is extracted with an equal volume of ethyl acetate for 3 hours; Or, in the step 3), the ratio of the combined concentrate to methanol is 0.5 g: 2 mL; Or, in the step 4), the chromatographic conditions of the high performance liquid chromatography are: The chromatographic column was a Waters Xbridge octyl decyl silane column, 4.6 × 150 mm, 5 μm; Flow rate: 1.0ml / min; Linear gradient elution was performed using a binary solvent system of water as phase A and methanol as phase B; The gradient elution conditions were as follows: Detector: Diode array detector, screening monitoring absorption wavelength between 190nm and 800nm; The eluate with a retention time of 16.2 min was collected, concentrated and dried to obtain the erythritol acid A; The eluate with a retention time of 16.3 min was collected, concentrated and dried to obtain the erythritol acid B; The eluate with a retention time of 14.2 min was collected, concentrated and dried to obtain the erythritol acid C; The eluate with a retention time of 14.3 min was collected, concentrated and dried to obtain the erythritol acid D.

6. The method for preparing the streptavidin acid AD according to claim 2 or 3, comprising the following steps: a) fermenting Streptomyces sp. FXJ1.172 to obtain a fermentation product; b) centrifuging the fermented product to collect mycelium; extracting the mycelium with anhydrous ethanol to collect the ethanol extract; c) concentrating and drying the ethanol extract to obtain a crude extract, gradient eluting the crude extract on a silica gel column (100-200 mesh) using a mobile phase having a volume ratio of CHCl3:CH3OH ranging from 95:5 to 70:30, and collecting eluted components; d) purifying the eluted fraction using a Sephadex LH-20 gel column, isocratically eluting with methanol, and collecting the methanol eluted fraction; e) separating the methanol elution component by reverse phase high performance liquid chromatography to obtain the erythritol acid AD; Preferably, in step b) of the method, the ratio of the mycelium to anhydrous ethanol is 1000 g:10 L, and the extraction time is 12 hours; Or, preferably, in step e) of the method, the chromatographic conditions of the high performance liquid chromatography are: The chromatographic column was a Supelco Ascentis C18 column, 100 × 21.1 mm, 5 μm; Mobile phase: acetonitrile / water (37:63, v / v), flow rate 2.0 mL / min; Detector: diode array detector; Detection wavelength: 220nm; HPLC retention time of the final product: erythritol acid A retention time = 9.2 min, erythritol acid B retention time = 11.1 min, erythritol acid C retention time = 6.0 min, erythritol acid D retention time = 7.4 min.

7. Use of any compound of the streptotriac acid AD according to claim 1 in the preparation of antibacterial drugs or in the prevention and treatment of potato scab.

8. The use according to claim 7, characterized in that: The antibacterial drug can inhibit the streptomyces pathogenic bacteria that cause potato scab; or, the potato scab is caused by the streptomyces pathogenic bacteria.

9. An antibacterial drug comprising at least one compound of the streptotric acid AD according to claim 1; Furthermore, the antibacterial drug can inhibit the pathogenic Streptomyces that causes potato scab.

10. A method for preventing and controlling potato scab, comprising applying an effective amount of at least one compound of the erythritic acid AD according to claim 1 to potato crops, potato crop seeds, soil or cultivation carriers.

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